[CQ-Contest] 15m monster finally up

Tõnno Vähk tonno.vahk at gafm.ee
Tue Sep 25 14:47:38 EDT 2012

I am happy to inform all friends that a project of last 4-5 years was
completed during the last weekend at ES5TV KO38CS central ES QTH and a
double H frame on 15m was finally erected what is probably one of the
biggest 15m setups in the world today.

See the full 2-day gallery at:


Go to the last 16th page if you wish to see the final product right awayJ

70 meters high tower carries 8 5-element 15m yagis as pairs separated
horizontally by 12 meter distance and vertical stacking is 14 meters. The
heights of the antenna pairs are 64, 50, 36 and 22 meters.

Antennas are Optibeam OB5-15:


Tower is produced by 4O3A/YT3M:


Model shows ca 16 dbd free space gain and almost 24 dbi gain at 4 degrees
over real ground. Beamwidth is less than 30 degrees. Testing has been so
far limited but the results confirm exactly the modelling results. Pattern
measured with signal generator and SDR was almost identical to what the
computer suggests and signal levels drop ca 12 db when antenna is 20
degrees off and already 20 db when 25 degrees off the correct direction.
There is huge -50db+ null at 90 degrees confirmed with real measurements
(!) and ca -20-30 db signal drop on the other directions.

First comparisons with my best antenna so far (4 high tribander stack) show
ca 10 db advantage to US when pointed right. That is huge of course.  At
the same time east coast and west coast can’t be covered with one directionJ

The stack will have phase switching capability which allows any pair of the
4 to be switched out of phase to change the radiation angle. Pre-configured
steps are 4, 7, 10, 15, 30 degrees while maintaining most of the gain as
all antennas are always connected. The phase switching is not yet connected
but will be very interesting to see the results and to get some real
insights into how the different angles play.

We briefly tried to hear the moonbounce when the moon was on horizon but
did not succeed yet. But 15m was wide open and signals probably did not
penetrate the ionosphere. I still hope to be able to complete some EME QSOs
with the stackJ

CQWW RTTY on the coming weekend will be the first contest for the monster.
Let me know how ES9C will sound on 15 meters. As the rotating is still
manual will keep it either to US or JA.




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